1. Field of the Disclosure
The present invention relates to methods for making and using well and pipeline treating fluids, and more specifically, to methods for hydrating and cross-linking water soluble polymers for use as well and pipeline treating fluids and the compositions resulting from these methods.
2. Description of the Related Art
The present application is directed to, among other things, methods for making and using fluids for treating wells and pipelines. For purposes of this application, a “well treating fluid” is a fluid used in a subterranean application, and “pipeline treating fluid” is a fluid used in a pipeline application. The term “treating” herein does not imply any particular action by the fluid or any component thereof. Examples of well treating fluids include fluid loss control compositions, hole-plugging compositions, displacement fluids, fracturing fluids and insulating fluids. Examples of pipeline treating fluids include a viscous pigging fluid and pipeline insulating fluids.
Providing effective fluid-loss control for well treating fluids is highly desirable. Fluid-loss control materials are additives specifically designed to lower the volume of a filtrate that passes through a filter medium. Most attain their fluid-loss control from the presence of solvent-specific solids, or from polymers that rely on filter cake buildup, or from polymers that rely on viscosity or viscoelasticity to inhibit flow into and through the formation. A variety of fluid-loss control materials have been used and evaluated, including foams, oil-soluble resins, acid-soluble particulates, graded salt slurries, linear polymers, viscoelastic fluid systems, and crosslinked polymers. Their respective comparative effects are well documented.
U.S. Patent Publication No. 2008/0026958 describes a variety of techniques that have been developed to control fluid loss. These include the use of “fluid-loss control pills,” which sometimes are referred to as “lost circulation pills.” Through a combination of viscosity, solids bridging, and cake buildup on the porous rock, these pills oftentimes are able to substantially seal off portions of the formation from fluid loss. They can also potentially enhance filter-cake buildup on the face of the formation to inhibit fluid flow into the formation from the wellbore.
Hole plugging fluids are also well known in the art. Sometimes in subterranean wells a hole can develop between the annulus and the production tubing. This can result in unwanted leakage of production fluid and/or fluids intended to flow through the production tubing into, for example, the packer annulus, and/or the unexpected leakage of the packer fluid or other fluids in the annulus into the production tubing. A solution to the problem is to place a hole-plugging material downhole across the hole or zone of fluid loss. The hole-plugging material is either formulated to be pre-cross-linked or to cross-link at downhole temperatures to seal the leak(s).
Another type of well treating fluid is known as an insulating fluid for an oil and/or gas well or pipeline. U.S. Pat. No. 6,908,886 provides examples of insulating fluids that are known in the art. Insulating fluids can have low thermal conductivities, while simultaneously meeting other constraints (e.g., regulatory or environmental constraints). These fluids can be facile to pump, yet can be capable of becoming more viscous after they are resident in situ within the annular space or one of the annular spaces in an oil and/or gas well, or pipeline.
A number of cross-linkable polymers are known for use in well treating fluids. These polymers can include hydratable polysaccharides, such as, for example, celluloses, which include derivatives of cellulose as described herein; and guars, which include guar and guar derivatives, such as carboxymethyl hydroxypropyl guar. A commonly used crosslinkable polymer for fluid-loss control pills are graft copolymers of a hydroxyalkyl cellulose that are prepared by a redox or redox initiated free-radical reaction with vinyl phosphonic acid. One example of this cross-linkable gelling polymer is known as SPECIAL PLUG, which is available from the Special Products Division of Champion Technologies, Inc., located in Houston, Tex.
A gel is formed by hydrating cross-linkable copolymers, such as those discussed above, in an aqueous fluid containing at least a trace amount of at least one divalent or multivalent cation. In some published processes, in order to hydrate the gelling polymer and make the cross-linked gel, a strong acid, such as HCl, can be added to the base fluid containing the gelling polymer. This mixture may be allowed to react for some length of time. The strong acid can reduce the pH to near zero and significantly promote polymer hydration, especially under shear. After polymer hydration, the pH of the polymer mixture can be increased to promote cross-linking of the gel.
However, it has been discovered that the strong acid used to promote polymer hydration of the gelling polymer at low pH can result in significant degradation of the polymer. For example, the low pH can result in the formation of a considerable amount of low molecular-weight gelling polymer. This can in turn reduce or eliminate the ability of the gel to cross-link and/or the resulting gel strength can be reduced. Further, when the polymers contact the subterranean formation, a low molecular-weight polymer can more easily move into the formation and cause undesired formation damage.
Furthermore, at the current cost of rig time, strong economic reasons, among others, exist to ensure that the cross-linkable polymer slurry can be fully, effectively and quickly hydrated, that the hydrated polymer can be fully, effectively and quickly cross-linked, and that the cross-linked polymer treating fluid can be fully, effectively and quickly delivered to the subterranean well or pipeline.
In addition, there are safety, regulatory and environmental concerns when working with strong acids, such as HCl. This can be especially true if the strong acid is used in combination with brines and/or for processing on an oil rig, especially offshore where space is limited and equipment for processing with strong acids may be unavailable or costly.
The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.